The present invention relates to a process for the production of degradation products of unsaturated fatty acids. These degradation products are volatile natural flavour and fragrance ingredients. These ingredients include but are not restricted to trans-2-cis-6-nonadienal, trans-2 cis-6-nonadien-1-ol, green note compounds such as cis-3-hexen-1-ol, trans-2-hexenal and improved complex flavour and fragrance mixtures such as natural plant extracts and absolutes. The above ingredients are present in a wide variety of fruits, leaves, vegetables and other plant constituents. Due to their pronounced impact on flavour and fragrance of these plants, they are widely used as impact ingredients in flavour and fragrance compositions. Their organoleptic characteristics range from fresh, grassy, "green", to cucumber- and melonlike.
Natural short chain, C.sub.6 -aldehydes and C.sub.6 -alcohols, the so-called "green note" compounds are currently isolated from plants or their essential oils (e.g. mint oil). They can also be biosynthetically produced. The FR-A1 2696 192 describes the production of ionones and aldehydes by contacting a natural source of polyunsaturated fatty acids with lipoxgenases, hydroxyperoxide lyases and a natural source of carotene in a liquid medium. The WO 95/26413 discloses the conversion of linolenic acid to cis-3-hexen-1-ol in presence of lipoxygenase, hydroperoxyde lyase and yeast. The degradation of polyunsaturated fatty acids according the state of the art is induced by the oxygenation reaction at cis-cis double bonds of these fatty acids. The oxygenation is catalyzed by lipoxygenase (EC 1.13.11.12)-enzymes. The oxygenated products, fatty acid hydroperoxides, are the precursors for many important hormones (e.g. prostaglandins) and of flavour and fragrance molecules. In plants, cleavage of the hydroperoxides occurs through the action of specific hydroperoxide lyases.
Natural C.sub.9 -aldehydes and C.sub.9 -alcohols (e.g trans-2-cis-6-nonadienal, trans-2-cis-6-nonadien-1-ol) as such are not available on the market and, so far, can only be used in flavour and fragrance compositions via the violet (Viola odorata L.) leaf absolute. The important constituents present in violet leaf extracts among others are: trans-2-cis-6-nonadienal, trans-2-cis-6-nonadien-1-ol, 1-octen-3-ol, cis-3-hexenyl alcohol and cis-3-hexenyl-acetate. All these compounds are derived from the oxidative degradation of fatty acids present in the violet leaves. The violet leaf absolute has a typical green fatty note similar to that of cucumbers and is predominantly used as fragrance component, but also as natural flavour ingredient in e.g. tropical fruit flavours for its fruity-cucumber character. Violet leaf absolute is therefore widely used in a great variety of flavour and fragrance compositions.
Due to the solubility characteristics of the absolute and the presence of other natural by-notes such as the flowery ionones and the fatty acids, it cannot be used in all requested dosages for flavour applications. It is therefore highly desirable to provide the above natural C.sub.9 -aldehydes and C.sub.9 -alcohols in a higher concentration with a relatively lower content of other by-notes.